In recent years there has been immense interest in preparing catalysts to produce linear low density polyethylene (LLDPE). Compared to conventional polymers of ethylene, LLDPE offers the following rheological and mechanical properties: high tensile strength, higher impact and puncture resistance, superior toughness, good organoleptics and low blocking, excellent clarity and gloss, and easy blends with other polyolefins. LLDPE can be obtained from the polymerization of ethylene by using Ziegler-Natta catalysts (zLLDPE) or by metallocene catalysts (mLLDPE), which are formed by the reaction of group 4 metallocene with a coactivator, of which methylalum(in)oxane (MAO) is most typical. In the case of conventional Ziegler-Natta catalysts, zLLDPE suffers in terms of clarity or stiffness, but by using metallocene catalysis, some long chain branching is introduced, which improves clarity, whereas mLLDPE is difficult to process into films. Incorporation of a small level of branching into the LLDPE leads to excellent processibility and high melt tensions suitable for film manufacture. Typically, LLDPE branching is achieved via copolymerization of ethylene with a linear α-olefin comonomer. LLDPE can also be obtained by single site constrained-geometry catalysts (CGCs), which are based on cooperative effects between active centers in multinuclear complexes.